1. Field of the Invention
This invention relates to a membrane and method for extracting hydrogen from fluids and, more particularly, this invention relates to a high-flow rate membrane and an improved method for extracting hydrogen from fluid without using electrical power or circuitry.
2. Background of the Invention
Global environmental concerns have ignited research to develop energy generation technologies which have minimal ecological damage. Concerns of global climate change are driving nations to develop electric power generation technologies and transportation technologies which reduce carbon dioxide emissions.
Hydrogen is considered the fuel of choice for both the electric power and transportation industries. While it is likely that renewable energy sources will ultimately be used to generate hydrogen, fossil-based technologies will be utilized to generate hydrogen in the near future.
The need to generate ever larger amounts of hydrogen is clear. Outside of direct coal liquefaction, other major industrial activities, such as petroleum refining, also require hydrogen. Collectively, petroleum refining and the production of ammonia and methanol consume approximately 95 percent of all deliberately manufactured hydrogen in the United States. As crude oil quality deteriorates, and as more stringent restrictions on sulfur, nitrogen and aromatics are imposed, the need for more hydrogen by the refining industry will increase.
Hydrogen production, as a consequence of other processes, is significant. A number of industries requiring hydrogen produce effluents containing significant amounts of unused hydrogen. However, this hydrogen requires clean-up prior to re-use. Furthermore, hydrogen is produced from the combustion of oil, methane, coal, and other petroleum-based materials. However, this hydrogen must be separated from other combustion gases, namely carbon dioxide, in order to be of use.
Petroleum refineries currently use cryogenics, pressure swing adsorption (PSA), and membrane systems for hydrogen recovery. However, each of these technologies has their limitations. For example, because of its high costs, cryogenics generally can be used only in large-scale facilities which can accommodate liquid hydrocarbon recovery. Membrane-based PSA systems require large pressure differentials across membranes during hydrogen diffusion. This calls for initial compression of the feed prior to contact to the upstream side of polymeric membranes and recompression of the permeate to facilitate final purification steps. Not only are these compression steps expensive, but PSA recovers less feedstream hydrogen and is limited to modest temperatures. U.S. Pat. No. 5,447,559 to Rao discloses a multi-phase (i.e. heterogenous) membrane system used in conjunction with PSA sweep gases.
Many membrane systems have been developed in efforts to efficiently extract target material from feed streams. Some of these membrane systems (U.S. Pat. Nos. 5,030,661, 5,645,626, and 5,725,633) are synthetic based, and incorporate polyimides and polyethersulphones. Unfortunately, such organic membranes are susceptible to chemical damage from H2S and aromatics. Such membranes also have limited temperature tolerance.
Other membrane systems (U.S. Pat. Nos. 4,857,080, 5,366,712, 5,652,020, and 5,674,301) require a multi-component approach wherein a hydrogen permeable metal, such as palladium or platinum overlays a porous ceramic substrate which is provided for strength. Such membranes have limited tolerance to elevated temperatures and are susceptible to chemical reaction with H2S. Furthermore, the multi-component, heterogenous nature of these membranes adds cost and lessens the reliability of any process which-uses them.
Proton-exchange membranes have high proton conductivities, and as such, are currently in development for fuel-cell applications and hydrogen pumps. One such application is disclosed in U.S. Pat. No. 5,094,927, issued to Baucke on Mar. 10, 1992. However, inasmuch as these membranes have relatively low electronic conductivities, they are not viable for hydrogen recovery scenarios, primarily because these membranes require the application of an electric potential to drive proton transport.
U.S. Pat. No. 6,066,592, issued to Kawae, et al. on May 23, 2000 discloses a ceramic support coated with palladium or a palladium alloy such as Pd-Ag to serve as a hydrogen separator.
U.S. Pat. No. 5,980,989, issued to Takahashi, et al. on Nov. 9, 1999 discloses a gas separator membrane in which a metal for separating a gas such as palladium or a palladium alloy is filled into pores opened on the surface of a porous substrate to close them.
U.S. Pat. No. 5,652,020 issued to Collins, et al. on Jul. 29, 1997 discloses a hydrogen-selective membrane comprising a tubular porous ceramic support having a palladium metal layer deposited on an inside surface of the ceramic support.
U.S. Pat. No. 5,518,530, issued to Sakai, et al. on May 21, 1996 discloses a hydrogen permeable palladium-silver alloy membrane supported on a porous ceramic substrate.
U.S. Pat. No. 5,332,597, issued to Carolan, et al. on Jul. 26, 1994 discloses at least a two layer membrane system: 1) a porous support layer, and 2) a porous multi-component metallic oxide layer. The multi-component metallic oxide layer is formed by deposition of an organometallic vapor in the pores of a porous substrate.
None of the aforementioned patents disclose a homogeneous mixture of ceramic and hydrogen transporting metals with no interconnected porosity.
A need exists in the art for materials which can be integrally molded to form a membrane for use to facilitate hydrogen extraction from a myriad of fluids. The materials, when combined, should produce a substrate having a high permeability to molecular hydrogen so as to facilitate nongalvanic (i.e. without the application of an external electric current) hydrogen separation from fluids. The substrate also should exhibit resistance to common materials found in hydrogen-laden feed streams. The materials should be derived from relatively common materials, and should be capable of being processed into a convenient reactor geometry, such as a tube or tape. In addition, the substrate should be chemically and mechanically stronger than proton-conducting ceramics and mechanically stronger than stand-alone metallic membranes which are susceptible to hydrogen embrittlement.
It is an object of the present invention to provide a hydrogen-separation membrane that over-comes many of the disadvantages of the prior art.
Another object of the present invention is to provide a membrane to extract hydrogen from a myriad of fluids. A feature of the invention is that the membrane possesses a high permeability to hydrogen at standard pressure and temperature conditions (i.e., approximately 1 atm and approximately 25xc2x0 C.). An advantage of the invention is that hydrogen separation occurs in a nongalvanic mode (i.e., without the use of electrodes or an applied electric field), primarily due to the inclusion in the membrane structure of a metal or a metal mixture which has good electronic conductivity and can dissolve atomic hydrogen. Another advantage is that the material is not easily xe2x80x9cpoisonedxe2x80x9d by carbon monoxide or other compounds present with hydrogen in effluent or process streams.
Yet another object of the present invention is to provide a hydrogen transfer membrane for use in a myriad of environments. A feature of the membrane is that the membrane is a homogenous phase comprised of ceramic and hydrogen-permeable metal, wherein the metal is evenly dispersed throughout the ceramic. An advantage of the membrane is that it has tolerance to high temperatures and various chemicals inherent with hydrogen-laden feedstream processing, such chemicals including H2O, H2S and CO2. Another advantage is its low cost of fabrication.
Still another object of the present invention is to provide a hydrogen-transfer membrane having no interconnected porosity. A feature of the invention is its high selectivity for hydrogen at the exclusion of other materials. An advantage of the invention is a three to four-fold increase in hydrogen permeation rates compared to ceramic-based substrates which are not homogenized with hydrogen transporting materials.
Another object of the present invention is to provide a method for separating hydrogen from a fluid. A feature of the present invention is the incorporation of a membrane having a high hydrogen permeability. An advantage of the invention is the utilization of the method in high temperature, chemically harsh environs without degradation to the membrane.
Briefly, the invention provides for a membrane for separating hydrogen from fluids by the transport of hydrogen atoms, the membrane comprising a sintered homogeneous mixture of a ceramic powder and a metal powder, wherein the membrane has no interconnected porosity.
Also provided is a method for extracting hydrogen from a fluid stream, the method comprising contacting the fluid stream to a metal that is dispersed throughout a non-proton-conducting ceramic.